Affiliation: Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America; Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.

ABSTRACTPlanar cell polarity (PCP) signaling controls the global orientation of surface structures, such as hairs and bristles, in both vertebrates and invertebrates. In Frizzled6(-/-) (Fz6(-/-)) mice, hair follicle orientations on the head and back are nearly random at birth, but reorient during early postnatal development to eventually generate a nearly parallel anterior-to-posterior array. We report the identification of a naturally occurring exon 5 deletion in Astrotactin2 (Astn2) that acts as a recessive genetic modifier of the Fz6(-/-) hair patterning phenotype. A genetically engineered Astn2 exon 5 deletion recapitulates the modifier phenotype. In Fz6(-/-);Astn2(ex5del/del) mice, hair orientation on the back is subtly biased from posterior-to-anterior, leading to a 180-degree orientation reversal in mature mice. These experiments suggest that Astn2, an endosomal membrane protein, modulates PCP signaling.

pgen.1005532.g001: The ridge phenotype.(A) Side and top views of a Fz6-/-;ridge/ridge mouse at approximately one month of age. Arrows indicate the single transverse ridge hair pattern on the back. (B-D) Hair orientation (red arrows) on flat-mounted back skins from WT, Fz6-/-, and Fz6-/-;ridge/ridge mice at P8. Images to the right of each flat mount correspond to the boxed regions labeled a-c and illustrate the correlation between vector scoring (red arrows) and the raw data (montage images showing follicle orientations). Rostral is at the top; caudal is at the bottom. The narrow slits and oval holes correspond to the locations of the eyes and ears, respectively. WT follicles are almost perfectly aligned in an anterior-to-posterior direction (B). Most Fz6-/- follicles are aligned in an anterior-to-posterior direction, except for a region in the mid-back (C). Fz6-/-;ridge/ridge follicles in the caudal half of the back exhibit a uniformly reversed (i.e. posterior-to-anterior) orientation (D). White scale bars, 1 mm.

Mentions:
This work began with the chance discovery of an unusual and stereotyped hair pattern among siblings in a Fz6-/- intercross, referred to hereafter as the ridge phenotype. This phenotype is characterized by a transverse ridge across the back, which arises when hairs in the upper back that are oriented in an anterior-to-posterior direction encounter hairs on the lower back that are oriented in a posterior-to-anterior direction (Figs 1 and S1). The ridge pattern is not observed in typical Fz6-/- mice. As seen in Figs 1 and S1, typical Fz6-/- back skins at P8 exhibit limited deviations from the strictly anterior-to-posterior follicle orientation of WT follicles.

pgen.1005532.g001: The ridge phenotype.(A) Side and top views of a Fz6-/-;ridge/ridge mouse at approximately one month of age. Arrows indicate the single transverse ridge hair pattern on the back. (B-D) Hair orientation (red arrows) on flat-mounted back skins from WT, Fz6-/-, and Fz6-/-;ridge/ridge mice at P8. Images to the right of each flat mount correspond to the boxed regions labeled a-c and illustrate the correlation between vector scoring (red arrows) and the raw data (montage images showing follicle orientations). Rostral is at the top; caudal is at the bottom. The narrow slits and oval holes correspond to the locations of the eyes and ears, respectively. WT follicles are almost perfectly aligned in an anterior-to-posterior direction (B). Most Fz6-/- follicles are aligned in an anterior-to-posterior direction, except for a region in the mid-back (C). Fz6-/-;ridge/ridge follicles in the caudal half of the back exhibit a uniformly reversed (i.e. posterior-to-anterior) orientation (D). White scale bars, 1 mm.

Mentions:
This work began with the chance discovery of an unusual and stereotyped hair pattern among siblings in a Fz6-/- intercross, referred to hereafter as the ridge phenotype. This phenotype is characterized by a transverse ridge across the back, which arises when hairs in the upper back that are oriented in an anterior-to-posterior direction encounter hairs on the lower back that are oriented in a posterior-to-anterior direction (Figs 1 and S1). The ridge pattern is not observed in typical Fz6-/- mice. As seen in Figs 1 and S1, typical Fz6-/- back skins at P8 exhibit limited deviations from the strictly anterior-to-posterior follicle orientation of WT follicles.

Affiliation:
Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America; Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.

ABSTRACTPlanar cell polarity (PCP) signaling controls the global orientation of surface structures, such as hairs and bristles, in both vertebrates and invertebrates. In Frizzled6(-/-) (Fz6(-/-)) mice, hair follicle orientations on the head and back are nearly random at birth, but reorient during early postnatal development to eventually generate a nearly parallel anterior-to-posterior array. We report the identification of a naturally occurring exon 5 deletion in Astrotactin2 (Astn2) that acts as a recessive genetic modifier of the Fz6(-/-) hair patterning phenotype. A genetically engineered Astn2 exon 5 deletion recapitulates the modifier phenotype. In Fz6(-/-);Astn2(ex5del/del) mice, hair orientation on the back is subtly biased from posterior-to-anterior, leading to a 180-degree orientation reversal in mature mice. These experiments suggest that Astn2, an endosomal membrane protein, modulates PCP signaling.